resolution problem (slow scrolling)

i realized a different resolution between IE7 and FF 3.6
IE7 has a smaller resolution but scrolls much faster
site here: www.obendorfer.at/cms

for some reason I can see your hosted demo on both browsers with the lower resolution which scrolls pretty much smoother.

I enclosed 2 screenshots for better illustration

I found out that this happened because of the FF zoom-settings. but I had opened up the demo and my site at the same time (in tabs) and they used different resolutions. where does this come from? can I set that somewhere?

Thank you!